THE ELIMINATION OF CHROMOSOMES IN THE MEIOTIC DIVISIONS OF BRACHYSTETHUS RUBROMACULATUS DALLAS

¹ Department of Zoology, Columbia University, New York

1. The fourth lobe in all testes of the pentatomid Brachystethus rubromaculatus shows an aberrant meiosis of a very definite character.

2. The first indication of this aberrancy is found in a chain formation and clumping of the autosomal tetrads just prior to metaphase. The two sex chromosomes are not included in this aggregation of autosomes.

3. At metaphase the X and the Y take a normal position in the spindle but the aggregate of autosomes is shunted laterally out of the middle region of the cell, away from the polar axis.

4. The two sex chromosomes divide equationally in the first division while the autosomal aggregate passes unaltered to either pole.

5. In the second division the X and Y again behave as in a normal meiosis and separate to opposite poles. The autosomal aggregate, if present, passes to either pole apparently at random.

6. Since the clumped autosomal tetrads pass undivided through both divisions while the sex chromosomes behave normally, the following four main types of spermatids are produced: X; Y; X + autosomes; Y + autosomes.

7. The mechanics and evolution of so constant an aberrancy are discussed.